Vessels are typically designed to be maneuverable when making sufficient headway such that movement of their rudders or steerable propulsion systems allows for directional change of the vessel. When operating in reverse, the maneuverability of such vessels is significantly hampered. In close quarter maneuvering, such as for docking purposes, the skill of the operator often makes the difference between safe docking or a dangerous situation since typical propulsion systems fail to address this situation. Docking is particularly difficult if there is any wind or current present. For this reason, most boaters view the docking of a vessel the most unpleasurable of boating experiences. Such experiences further inhibit inexperienced boaters from enjoying the water in all but the most calm conditions.
Bow and stern thrusters have been made available, but require a level of skill to operate in that an operator must control the thruster in addition to the main propulsion systems. This coordination has made the present use of thrusters limited to only the most un-maneuverable vessels and experienced captains.
Today, the most efficient high speed marine propulsion systems use surfacing propellers. The typical surfacing propeller system is transom mounted and allows adequate forward handling but only marginal handling in reverse. The typically surfacing propellers change the direction of the thrust by turning the entire drive assembly on the stern of the boat to push the stern port or starboard. These surfacing drive systems are both complicated and expensive in that they require large mechanical systems to be mounted aft of the transom of the boat.
U.S. Pat. No. 4,689,026 (the contents of which are herein incorporated by reference), teaches a marine surface drive system which incorporates surface piercing propeller technology beneath the hull of a vessel. As with any fixed propeller system, such propulsion systems lack adequate directional control when reverse thrust is employed. The propeller tunnel vertical walls further complicate the problem since their surfaces make pushing the transom of the boat to port or starboard more difficult due to the additional effort required to move a vertical surfaces sideways in the water.
U.S. Pat. No. 5,016,553 to Spencer discloses a vector control steering system which utilizes a transom mounted thrusting device which is integrated with a stern mounted main drive system. Such a system would not cure the deficiencies of a tunnel mounted surface piercing propulsion system such as Small's because of the increased effort required to move the vessel's stern laterally.
Most marine vessels require a lateral stabilizing force at their aft end to minimize the tendency at high speed for a "spin out". In a "spin out" the vessel spins uncontrollably regardless of corrective action taken by the operator. To control this tendency some form of lateral resistance is employed.
The easiest way to understand this is to look at a weather vane. Weather vanes have a large area behind the axis of rotation to keep the pointed end always pointing into the wind. Boats are no different. They need a large area behind their axis of rotation (the center of gravity) to keep their nose pointed in the right direction and avoid "spin out". The most common method of providing this source of lateral resistance is a rudder. While rudders provide steerage they also provide stability and resistance to lateral motion.
Spencer overlooks this conflict of design; instead of providing the thrust application at the front of the boat where lateral resistance to motion is the least, he proposes thrusting laterally at the rear of the vessel where the inherent resistance to lateral motion is the greatest and the application of a thruster the least effective. While it would be possible to steer the boat with his approach the cost of such a system would be far greater than if the thrust were applied to the bow. History bears this out as there are no commercially available transom thrusters in use today.
Numerous prior art patents have utilized auxiliary thrusters, for example: U.S. Pat. No. 5,522,335 discloses a combined azimuthing and tunnel auxiliary thruster for a vessel. U.S. Pat. No. 5,642,684 is directed toward a thrust directing unit for a marine vessel comprising a diverging wall outlet with adjustable deflector vanes contained therein and an adjustable water jet flow. U.S. Pat. No. 5,501,072 discloses a combined centrifugal and paddle-wheel side thruster for boats. U.S. Pat. No. 5,282,763 teaches a steerable bow thruster useful for swath vessels. These thrusters utilize a motive force device to provide a supply of pressurized water which is directed through rotatable outlets. U.S. Pat. No. 5,146,865 discloses a water jet propulsion system for shallow draft vessels. U.S. Pat. No. 5,129,846 teaches a vessel propulsion system including longitudinally spaced forward and rear zones including forwardly and rearwardly directed jet openings in combination with a pump and controllable valving system for providing propulsion and steerage. U.S. Pat. No. 5,090,929 provides paired spaced electrically driven motors at the transom for steering and propelling small boats.
U.S. Pat. No. 4,580,517 is directed toward a vessel having parallel hulls and thrustable which are rotatable through 360 degrees of rotation. U.S. Pat. No. 4,419,082 describes a driving and controlling device including a water-jet drive mechanism for shallow draft vessels. U.S. Pat. No. 4,377,981 teaches a lateral thrust rudder for ships including a cross channel which traverses the ship from one side to the other and a propeller mounted within the cross channel. U.S. Pat. No. 4,315,476 teaches a steering system for ships incorporating a propeller in a flow duct having deflectors for directing flow to one side of the vessel or the other. U.S. Pat. No. 5,896,016 is drawn to a process for optimizing the real power levels by regulating the rotational speed of both bow and stern mounted propellers, e.g. in a vessel such as a ferry having independent bow and stern drive systems.
What is lacking in the art is a coordinated bow propulsion system for enhanced maneuverability of vessels moving at low speeds or when using reverse thrust. In a particularly desirable embodiment, the enhanced propulsion system would be incorporated in such a manner that it became invisible to the driver by actuating the bow thruster in coordination with the vessel's steering wheel and shift lever.